The present application is directed to an electronic copier or printer of the type which uses a multi-beam raster output scanner (ROS) to form images on a photoreceptor surface. More particularly, the application is directed to spatial filters located in the optical path of the ROS to compensate for imperfections and/or errors in the operation and/or manufacture of the ROS system.
For example, solid area non-uniformity, line growth, and banding, as well as other undesirable image defects may occur when ROS technology is employed to generate an image. These image quality defects are objectionable and lead to costly ROS designs. To address these issues a low cost banding reduction solution via optical filtering was introduced in U.S. Pat. No. 4,884,083, entitled, “Printer Compensated for Vibration-Generated Scan Line Errors,” by Loce et al., issued Nov. 28, 1989, incorporated herein in its entirety.
Loce et al. disclose a printing system employing a raster output scanning (ROS) device which incorporates compensation for the effects of motion of the medium upon which an image is being printed. More particularly an amplitude transmittance spatial filter is positioned either in the “slow scan” exit pupil of the optics of the system or in the first Fourier transform plane of the scanning optical system.
Many modern laser scanners use 1-D and 2-D arrays of beam generators. It is therefore desirable to have a low cost optical filtering method and apparatus for image error reduction that works with and addresses imaging issues for multiple-beam scanning systems.